// "Hello World"也可以作为类型的，叫做字面量类型
const message: "Hello World" = "Hello World";

let num: 123 = 123;
// num = 321;

//字面量类型的意义，就是必须结合联合类型
type Alignment = "left" | "right" | "center";
let align: Alignment = "left";
align = "right";
align = "center";
